The invention concerns a process for producing any photoluminescent printed polychromatic image (namely one which can incorporate all the shades of colours and various forms possibly including continuous variations of colours (shaded, fading etc., shadows, intensity variations, mottled effects etc.) invisible under illumination with visible light and visible under illumination by at least one source of invisible light, designated hereinafter in all the text as xe2x80x9cany photoluminescent printed polychromatic imagexe2x80x9d.
xe2x80x9cVisible lightxe2x80x9d designates a light of which the spectral composition is situated in the visible spectrum from 0.4xcexc to 0.8xcexc. xe2x80x9cInvisible lightxe2x80x9d designates a light of which the spectral composition is situated outside the visible spectrum, in particular in the ultra violet and/or the infra red spectrum.
Photoluminescent printed monochromatic markings which are invisible under illumination with visible light and visible under illumination with invisible light (ultraviolet or infra red) are often used for the purpose of the authentication of documents such as bank notes. Different printed monochromatic markings may be juxtaposed and/or superimposed, which create spots of colours composed of a finite number and in a discontinuous manner.
Nevertheless, these photoluminescent monochromatic markings do not make it possible to produce a true photoluminescent printed polychromatic image reproducing, with all the shades of colours and forms, any polychromatic image visible in visible light such as a photographic image which is not in half-tone and is non-digitized.
Any photoluminescent printed polychromatic image of this type may be of value in many fields and may have various applications, in particular as an authentication element and/or for the purposes of decoration.
As regards authentication, any photoluminescent printed polychromatic image may provide at least three levels of authentication: printing the image creates raised patterns and/or an opalescence visible in visible light; under illumination in invisible light, it is possible to verify the conformity of the image which is extremely difficult to counterfeit perfectly taking into account its complexity and the fact that it is applied to the background of a document provided with other designs visible by transparency, unless the original is available which is visible under visible light, reproduction from the image visible in invisible light not providing the original image; and spectrophotometric analysis enables the photoluminescent compounds used to be identified and therefore their authentic character.
For decorative purposes, any photoluminescent printed polychromatic image of this type proves to have a an unusual special appearance when illuminated in invisible light.
However, various attempts to produce a photoluminescent printed polychromatic image of this type which date back more than sixty years have ended in failure.
In particular, traditional printed polychromatic images visible in visible light are generally produced in quadrichrome (yellow, magenta, cyan, black) on a white background. The original image is filtered with three coloured filters (blue, green, red) having a spectral pass-band of 100xcexc (a third of the visible spectrum). The appearance of colours on the printed image is due to the reflection of natural visible light (daylight or an illuminating lamp) by the printed substrate through the transparent coloured inks which selectively absorb the incident light according to the so-called xe2x80x9cmaterial colourxe2x80x9d principle by subtractive synthesis. For each coloured ink, the substrate reflects two thirds of the visible spectrum, according to a complementary spectral composition of the absorption spectrum of the ink in the visible region. With this technique, it is not possible to produce a photoluminescent printed polychromatic image. Indeed, if photoluminescent pigments are used corresponding to the fundamental colours of the coloured filters used for printing in quadrichrome, in inks which are printed from three negatives obtained after filtering with the aid of traditional coloured filters, it is not possible in practice to reproduce the polychromatic image in a photoluminescent manner, reliably and with good quality.
U.S. Pat. Nos. 2,302,645, 2,277,169 and 2,434,019 thus describe various attempts to produce images with the aid of fluorescent pigments.
Nevertheless, the processes described in these documents do not make it possible to produce a photoluminescent printed polychromatic image by automatic and reliable reproduction of a polychromatic image. Indeed, the processes described in these documents consist of manually producing, in the first instance, a trichromatic positive. Subsequently, this trichromatic positive is used to be reproduced by printing with the aid of inks, certain of which incorporate fluorescent pigments. As a consequence, these documents show that the automatic obtaining of a trichromatic photoluminescent positive has been abandoned, since these documents consider that the positive is out of necessity produced manually.
Equally, the document R. J. TUITE xe2x80x9cFluorescent multicolor additive systemxe2x80x9d XP 002108747, PRODUCT LICENSING INDEX, no84, pages 81-85, INDUSTRIAL OPPORTUNITIES LTD, HAVANT, GB ISSN: 0374-4353, April Issue, 1971, teaches the production, by printing with the aid of a gravure plate press, of a multicoloured image which is fluorescent under ultraviolet light. The process used in this document consists of producing negatives with red, green and blue separation from a continuous positive by exposure through a red, green and blue filter, respectively. With this process, since each of the negatives has not been finely filtered, the largest proportion of the area of the final image includes an abnormal surcharge of the three colours forming a dominant white. On account of this, the fluorescent image obtained is extremely pale and is in practice either invisible or a xe2x80x9cphantomxe2x80x9d image, in spite of the production of a large number of successive final layers of green ink.
The object of the invention is therefore in a general manner to enable any photoluminescent printed polychromatic image to be produced. Accordingly, the object of the invention is to make it possible to reproduce in a printed photoluminescent form and in an automatic and reliable manner, any original polychromatic photographic image formed by subtractive synthesis (material colour principle) and which is visible in visible light (printed, painted, photographic image etc).
The invention also aims at providing a simple and low-cost process for rapidly obtaining and reproducing such an image on the industrial scale, automatically and reliably, in particular in a manner similar to traditional printing techniques, without requiring the manual production of a trichromic positive by an artist, and while providing a high quality and high contrast image.
The invention also aims at providing applications for any kind of photoluminescent printed polychromatic image.
To this end, the invention concerns a process for producing any photoluminescent printed polychromatic image invisible under illumination in visible light and visible under illumination by at least one source of invisible light, wherein:
an original polychromatic image 1, visible in visible light, is chosen or is produced by subtractive synthesis (material colour principle),
at least one set of at least three images, known as filtered images, is produced and recorded by filtering the original image,
at least one set of at least three images, known as printed images, is printed separately one after the other and one above the other, by using and reproducing respectively one of the filtered images, with a printing composition containing a photoluminescent pigment, the different photoluminescent pigments of the different printed images of the same set emitting, under illumination by at least one source of invisible light, colours capable of forming all the colours of the visible spectrum by additive synthesis,
wherein:
filtered images, known as monochromatic filtered images, are produced by filtering the original image in a spectral pass-band lower than or equal to 15 nm centred on a wavelength, known as the filtering wavelength, chosen from the wavelengths of at least three fundamental colours, the different filtering wavelengths of the monochromatic filtered images being distinct in pairs and being adapted so as to enable all the colours of the visible spectrum to be formed by additive synthesis, each of these filtering wavelengths being at least approximately equal to a wavelength of an emission peak of a photoluminescent pigment under illumination by at least one source of invisible light,
each printed image, called the monochromatic printed image, is printed by using and reproducing one of the monochromatic filtered images with a printing composition containing a photoluminescent pigment having an emission wavelength peak under illumination by at least one source of invisible light, which is at least approximately equal to the filtering wavelength used for obtaining the said monochromatic filtered image.
xe2x80x9cAt least approximately equalxe2x80x9d means either perfect equality between wavelengths or the fact that the wavelengths are sufficiently close for their difference to produce no appreciable effect on the image obtained. In particular, the wavelength of the emission peak may be situated in all the pass-band below or equal to the filtering wavelength, to within 15 nm. In other words, a certain margin of error is accepted for wavelengths and this margin of error is of the order of the pass-band of the filters used.
Advantageously, a process according to the invention is also characterized by at least one of the following characteristics :
in order to produce each of the monochromatic filtered images, an original of any original polychromatic image visible in visible light is illuminated, and the polychromatic image reflected by this illuminated original is filtered in a spectral pass-band below or equal to 15 nm centred on the filtering wavelength of the fundamental colour corresponding to the monochromatic filtered image and, advantageously, the reflected polychromatic image is filtered with pass-band filters having a spectral pass-band of the order of 10 nm, in particular interference pass-band filters;
there are chosen, by way of filtering wavelengths and emission peaks of the photoluminescent pigments (by selecting suitable filtering means and photoluminescent pigments) of different monochromatic printed images of the same set forming a reproduction of an original image, at least one wavelength in the green region, at least one wavelength in the red region and at least one wavelength in the blue region; and advantageously, wavelengths are chosen adapted so that they are separated by the same spectral distance of between 80 nm and 100 nm, in particular equal to 90 nm; in particular a wavelength in the green region of between 520 and 570 nm, a wavelength in the red region of between 610 and 680 nm and a wavelength in the blue region of between 430 and 480 nm;
the monochromatic printed images are printed so that, in the order in which the illuminating light is received, they exhibit the filtering wavelengths and the emission peaks of the photoluminescent pigments in the order blue, red and green and the monochromatic printed images are printed one on the others without an intermediate layer;
for the same set forming a reproduction of an original polychromatic image, only three monochromatic printed images are printed, one in green, one in red and one in blue, and each monochromatic printed image is printed in a single print layer;
in order to produce and record each monochromatic filtered image, the filtered image is captured by charge transfer photosensitive means, CCD, a corresponding digitized image is recorded and there is formed, from each monochromatic filtered image, a half-tone image which is then used to print the monochromatic printed image, and advantageously the half-tone image has a half-tone of 60 to 133, in particular of the order of 80 (this value corresponding to the number of lines or dots per inch (2.54 cm);
the different monochromatic printed images of the same set are printed at least substantially with the same print thickness; each monochromatic printed image is printed so that the quantity of photoluminescent pigment at each point is a function of the luminous intensity of the original polychromatic image at this point according to the corresponding filtering wavelength (this function being proportional in the case of a positive and inversely proportional in the case of a negative); and photoluminescent pigments are used having a purity factor (ratio of the quantity of monochromatic light according to the dominant wavelength of the emission peak to the sum of this quantity of monochromatic light and the quantity of emitted white light) equal to 1, virtually monochromatic light having a main emission peak or monochromatic light having a single emission peak;
each monochromatic printed image is allowed to dry and/or harden after it has been printed and before another monochromatic printed image is printed;
in order to produce the same set of monochromatic printed images, pigments are used which are photoluminescent under illumination by one and the same source of invisible light and as a variant, in order to produce the same set of monochromatic printed images, at least one first pigment is used which is photoluminescent under illumination by at least one first source of invisible light, and at least one second pigment which is photoluminescent under illumination by at least one second source of invisible light with a wavelength or with wavelengths distinct from that or those of the first source of invisible light;
a set is printed of monochromatic printed images which are positive images of an original image, adapted so as to reproduce a positive of the original image by additive synthesis;
a set is printed of monochromatic printed images which are negative images of an original image, adapted so as to reproduce a negative of the original image by additive synthesis;
a first set of positive monochromatic printed images is printed with pigments which are photoluminescent under illumination by a first source of invisible light (in particular infrared or ultraviolet light) and a second set of negative monochromatic printed images is printed with pigments which are photoluminescent under illumination by a second source of invisible light with a wavelength which is distinct from that of the first source of invisible light, in particular infrared or ultraviolet;
the wavelengths of the emission peaks of the photoluminescent pigments used to print the first set are at least approximately equal to the wavelengths of the emission peaks of the photoluminescent pigments used for printing the second set, so that the same monochromatic filtered images can serve to print the two sets;
there is additionally printed at least one image, known as an infrared image, with a printing composition containing at least one pigment having at least one peak emission wavelength situated in the infrared region but with no emission in the visible light region when this pigment is activated by illumination under a source of visible light; the infrared image is a monochrome image which may be of the same nature (positive or negative) as the monochromatic printed images or, preferably, of the opposite nature; it is also possible to provide a first positive set and a second negative set, as indicated above, and a positive or negative infrared image;
in order to print each monochromatic printed image a printing composition is used which incorporates a photoluminescent pigment but which is, at least after drying, transparent or translucent for visible light when placed under illumination by the source of invisible light or by each of the sources of invisible light and in addition, advantageously, in order to print each monochromatic printed image, a printing composition is used which is, at least after drying, transparent or translucent for visible light when placed under illumination in visible light;
the monochromatic printed images are printed by screen printing and advantageously a printing composition is used formed of a screen printing varnish polymerizable under ultraviolet radiation, and a printing screen is produced from each monochromatic filtered image and different printing screens are produced from the same fabric;
pigments are used which are photoluminescent under illumination by at least one source of invisible light of which the spectral composition is situated in the ultraviolet or infrared regions;
inorganic photoluminescent pigments are used, in particular of the family of rare earths, and as a variant organic photoluminescent pigments are used with better transparency (least opalescence) but which are less durable than inorganic pigments;
the monochromatic printed images are printed successively on the free outer face of a transparent film in the visible region including at least one layer formed of a continuous impression of a printed composition, for example a film such as described in EP-0 271 941 or U.S. Pat. No. 5,232,527.
The invention thus makes it possible to obtain, for the first time, any photoluminescent printed polychromatic image automatically which is a true reproduction, with all the shades of colours and forms which can vary infinitely in a continuous manner, from an original of any original polychromatic image visible in visible light. This original may be printed or may be a memorized analog image (photographic, cinematographic, video..) or a digitized image memorized on a computer bulk memory or another.
It should be noted that this result is not obtained by using wide band filtration as in traditional printing but on the contrary selective filtration with a narrow band in visible light and a trichromatic additive synthesis under illumination in invisible light.
The invention also extends to the printed image obtained by a process according to the invention.
The invention thus concerns any photoluminescent printed polychromatic image invisible under illumination in visible light and visible under illumination by at least one source of invisible light, including at least one set of at least three images, known as printed images, printed one above the other, each printed image including a photoluminescent pigment emitting a colour under illumination by a source of invisible light, the different colours of the printed images of the same set being adapted so as to be able to form by additive synthesis all the colours of the visible spectrum under illumination by at least one source of invisible light, wherein each printed image, known as the monochromatic printed image, corresponds to the filtration of an original polychromatic image by subtractive synthesis visible in visible light, in a spectral pass-band below or equal to 15 nm centred on a wavelength, known as the filtration wavelength, chosen from the wavelengths of at least three fundamental colours, the different filtration wavelengths being distinct in pairs and adapted so that they can form all the colours of the visible spectrum by additive synthesis, each of these filtration wavelengths being at least approximately equal to a wavelength of an emission peak of the photoluminescent pigment of the corresponding monochromatic printed image.
Advantageously, an image according to the invention is also characterized by at least one of the following characteristics:
it includes at least one monochromatic printed image having at least one emission peak wavelength in the green region, at least one monochromatic printed image having at least one emission peak wavelength in the red region and at least one monochromatic printed image having at least one emission peak wavelength in the blue region; and for the same set of monochromatic printed images forming a reproduction of an original image, it comprises three monochromatic printed images, one in the green, one in the red and one in the blue region;
the wavelengths of the emission peaks of the monochromatic printed images are separated by the same spectral distance of between 80 nm and 100 nm, in particular of the order of 90 nm; and advantageously they comprise a monochromatic printed image having an emission peak wavelength in the green region of between 520 and 570 nm, a monochromatic image having an emission peak wavelength in the red region of between 610 and 680 nm and a monochromatic printed image having an emission peak wavelength in the blue region of between 430 and 480 nm;
the monochromatic printed images of the same set follow each other, in the order in which the light is received, in the order blue, red, green of the wavelengths of the emission peaks and advantageously the monochromatic printed images are stacked on each other without an intermediate layer, the monochromatic printed images having at least substantially the same print thickness;
each monochromatic printed image is formed of a printing composition which is transparent or translucent for visible light when it is placed under illumination by the source of invisible light, or by each of the sources of invisible light, and which incorporates a photoluminescent pigment, each monochromatic printed image being formed of a printing composition which is transparent or translucent for visible light when it is placed under illumination in visible light;
the photoluminescent pigments of at least the same set of monochromatic printed images emit under illumination by at least one source of invisible light of which the spectral composition is situated in the ultraviolet or infrared regions; the different monochromatic printed images of the same set include photoluminescent pigments emitting under illumination by at least one source of invisible monochromatic light; advantageously, the different photoluminescent pigments of at least the same set of monochromatic printed images are adapted so as to have an emission peak wavelength under illumination by one and the same source of invisible light; and as a variant, for at least the same set of monochromatic printed images, at least one first pigment is photoluminescent under illumination by at least one first source of invisible light, and at least one second pigment which is photoluminescent under illumination by at least one second source of invisible light with a wavelength or wavelengths distinct from that or those of the first source of invisible light;
it comprises several sets of monochromatic printed images visible under illumination by different sources of light (for example one set forming a reproduction visible under ultraviolet light and one set forming a reproduction visible under infrared light);
it comprises a first set of positive monochromatic printed images including pigments which are photoluminescent under illumination by a first source of invisible light, in particular ultraviolet or infrared light, and adapted so as to reproduce a positive of an original polychromatic image by additive synthesis, and a second set of negative monochromatic printed images including pigments which are photoluminescent under illumination by a second source of invisible light with wavelengths distinct from that of the first source of invisible light, in particular ultraviolet or infrared light, and adapted so as to reproduce a negative of an original polychromatic image by additive synthesis, these two sets being capable of being superimposed and being reproductions of the same polychromatic original image, one negative and the other positive, and as a variant being reproductions of two different original images;
it additionally includes at least one image, known as an infrared image, visible in the infrared region but invisible in the visible light region under illumination by a source of visible light; it being possible for this infrared image to be an inverse reproduction of an original polychromatic image produced by a set of monochromatic printed images on the same substrate, and to be capable of being superimposed on this set.
The invention also extends to applications for an image according to the invention. The invention extends in particular to the application of an image according to the invention for the protection of a document, in particular a passport, an identity card, a driving licence, a vehicle registration document or other official document for identification and/or authentication, a fiduciary document such a bank note, a cheque, a card or other document of payment.
The invention thus concerns a device for protecting a document including at least one transparent protective film for covering and protecting at least a portion of the area of a document, in which the film includes at least one image according to the invention.
The invention also concerns a document, in particular a passport, an identity card, a driving licence, a vehicle registration document or other official document for identification and or authentication, a fiduciary document, a bank note, a cheque, a card or other document of payment, including at least one image according to the invention. Advantageously and according to the invention, at least one image according to the invention is carried by at least one transparent protective film applied on at least one face of the document.
The invention also concerns a process, any photoluminescent printed polychromatic image, a protective device and a document characterized in combination by all or part of the characteristics mentioned above or hereinafter.